1. Field of Invention
The field of invention relates to active type vibration control devices which protect building structures from damage due to seismic shock and/or high winds.
2. Description of Related Art
A dynamic damper (hereinafter designated as DD) is available as a vibration control device of the passive type, as shown in Japanese Pat. Laid-open No. 63-76932 and Japanese Pat. Publication No. 3-38686.
FIG. 4 of the present application shows a prior art vibration model of a DD as applied to a building structure having a mass m.sub.1, comprising a main vibration system, and an additional mass body m.sub.d, comprising a damping system. The building structure, having a spring constant k.sub.1, and the additional mass body m.sub.d are connected through a spring having a spring constant k.sub.d and a damper having a damping coefficient c.sub.d. Displacement of the structure is indicated by x.sub.1, and x.sub.d represents a displacement of the additional mass body.
A natural angular frequency of the main vibration system is given by: EQU .omega..sub.1 =(k.sub.1 /m.sub.1).sup.1/2
In the DD, a mass m.sub.d of the damping system is designed so that the ratio of the mass m.sub.d to the mass m.sub.1 of the main vibration system may be set as shown: EQU .mu.=m.sub.d /m.sub.1 .gtoreq.0.01.
At this time, the natural angular frequency of the damping system is given by: EQU .omega..sub.d =(1/1=.mu.).omega..sub.1
A damping coefficient c.sub.d and a damping factor h.sub.d are respectively represented by: EQU c.sub.d =2m.sub.d .omega..sub.d h.sub.d EQU h.sub.d =[3.mu./8(1+.mu.)].sup.1/2
There is also known in the prior art a device called an Active Mass Driver (hereinafter AMD), which is a vibration control device of an active type, such as shown in U.S. Pat. No. 5,022,201.
FIG. 5 shows a prior art vibration model of an AMD, which applies a control force u(t) provided by hydraulic pressure or electromagnetic force, or the like, from an actuator between the building structure, having a mass m.sub.1, and an additional mass body, having a mass m.sub.d, to actively control the vibration of the building structure.
In the AMD, assuming that a spring between the building structure and the additional mass body, constituting a vibration control device, is set under a soft condition, i.e., EQU .omega..sub.d .ltoreq.(1/1).omega..sub.1
the control force u(t) is given in the following equation: EQU u(t)=G.sub.1 (dx.sub.1 /dt)+G.sub.2 (dx.sub.d /dt)
wherein G.sub.1 is a gain in a circuit including an AGC circuit or the like against the response speed of the structure to obtain corresponding large inputs from small inputs. The second term in the above equation gives a damping property to the additional mass body as well as stability thereof by adding the product of a gain G.sub.2 (negative sign) to a vibration speed of the additional mass body by the control force.
Active tuned mass dampers (ATMD hereinafter) have been made which add a spring, having a spring constant k.sub.d, in parallel with the control force provided by an actuator, as shown in the vibration model of FIG. 6 to obtain a vibration control effect to the same degree as an AMD, but by means of less control force in comparison with that of the AMD.
In the case of an ATMD, a spring constant k.sub.d is set so that the vibration of an additional mass body may synchronize with that of the building, that is, EQU .omega..sub.d =.omega..sub.1
and the resulting control force u(t) is, for example given by the following equation: EQU u(t)=G.sub.1 (dx.sub.1 /dt)+G.sub.2 (dx.sub.d /dt)+G.sub.3 (x.sub.1 -x.sub.d)
wherein G.sub.3 is a gain having a negative sign and cancels a part of the inertial force applying on the additional mass body at a vibration time to the third term in the above equation so that the additional mass body may be vibrated by less control force.
Furthermore, there is a disclosure in Japanese Pat. Publication No. 3-70075 showing means for controlling the vibration of a building structure due to an earthquake or the like by an extremely small control force. A second additional mass body, having a mass less than that of the first mentioned additional mass body, is connected to the first mentioned additional mass body of the DD through a spring. An actuator applies a control force to the second additional mass body. The mass of the second additional mass body is selected so as to obtain a higher vibration control effect by a far smaller control force in comparison with the AMD or ATMD. However, this system has problems such as vibrations and noise produced by the first and/or the second additional mass body, similar to vibration and noise problems associated with AMD and ATMD systems. Further, the AMD and ATMD systems present both maintenance problems and installation and space problems, which should be considered in selecting a vibration control system to protect a building structure.
The present invention provides solutions to these problems, and additionally provides a vibration control system with high reliability, safety, and efficiency in operation and maintenance.